1. Field of the Invention
This invention relates to an improved process for preparing the hot metal portion of the charge to a steelmaking process; more particularly, to a process for substituting molten scrap for a portion of the molten blast furnace iron typically used to formulate the charge to a steelmaking process.
2. Description of the Prior Art
Modern steelmaking processes, such as the basic oxygen process (BOP) and more recently the bottom blowing process known as Q-BOP, still consume large quantities of molten iron (hot metal) produced by the conventional blast furnace. In most steel plants, the hot metal portion of the metallic charge to the steelmaking furnace is about 70%, with the balance cold or preheated scrap. Any adverse changes that may occur to the hot metal between the time it is cast at the blast furnace and the time it is charged to the steelmaking furnace are the subject of concern to the steelmaker.
Hot metal must be conveyed from the blast furnace to the steel plant in some type of container, often a refractory lined vessel known as a submarine ladle. Despite recent efforts toward conserving the sensible heat of the hot metal during periods of transit, storage or transfer from one container to another, a certain amount of temperature loss is inevitable; typically, this amount is in the range of 350.degree. F. to 375.degree. F. As the temperature of the hot metal decreases, carbon in the solution in the metal is precipitated according to well-known principles and is expelled as kish. In a typical situation, where the hot metal is cast at the blast furnace at a temperature of about 2775.degree. F. and is charged to the steelmaking vessel at 2400.degree. F., the temperature loss of 375.degree. F. results in a carbon loss of about twelve percent, e.g., from 5.10% C. to 4.50% C.
Carbon, of course, is the primary source of oxidizable fuel in the hot metal. The reaction between carbon in the hot metal and the gaseous oxygen used in pneumatic steelmaking processes is highly exothermic and thus permits the process to be autogenous. A loss of carbon on the order of twelve percent in hot metal produced by a blast furnace is therefore a very expensive loss.
There exists, therefore, a need to minimize carbon loss in hot metal, given the almost inevitable temperature loss that will occur between the blast furnace and the steelmaking vessel.